Pittsburgh police remained on the scene hours after the incident, which was reported at about 2:20 a.m. Tuesday on Merritt Avenue in Carrick.

"I don't know if they knew each other personally, but I knew they knew of each other, and for that to happen, it's a horrible, horrible thing," said Michael Ferita, who knows all of the people involved in the incident.

Public Safety spokeswoman Sonya Toler said two men entered the first-floor apartment with guns and fired shots into the residence before pushing the tenant from the living room into the bedroom and saying, "We want your stuff."

The 19-year-old man who lives in the apartment with his 17-year-old girlfriend grabbed a shotgun that he keeps in his bedroom and fired three shots, striking both of the alleged intruders, Toler said.

One of the men who was shot died. He was identified as David Calhoun, 31, of Pittsburgh.

Police identified the other man as Christopher Thomas, 27, of Marshall-Shadeland, and said he was taken to UPMC Mercy hospital and arrested on charges of carrying a firearm without a license, persons not to possess a firearm, aggravated assault, burglary, robbery and criminal conspiracy. Police also said there was a city warrant for his arrest connected to a rape in April.

The young man who fired the fatal gunshot was not injured. Police have not identified him publicly while the investigation continues.

"He's one of the most laid-back, chill, hippie kids. You know? Like, he loves everybody. I've never seen the kid raise his voice, let alone fire a gun. That's not like him at all," Ferita said.

The incident happened near the filming location for "Southpaw," a movie starring Jake Gyllenhaal that has been shooting in the Pittsburgh area.